System and method for sensor less magnetic field control of a motor

Abstract

A system and method for sensor less control of a stepper motor is described. The system and method includes estimation of the position of a rotor of the motor by way of sensing circuitry on the windings of the motor, without the use of positional sensors. The system and method of stepper motor control further includes magnetic field optimization for increasing the torque generating component of a magnetic field generated by stators of the motor, and magnetic field weakening for countering some of the effects of back electromotive force generated by the magnetic rotor.

Description

[0001]This application claims the benefit of U.S. Provisional Application No. 60 / 603,287, filed Aug. 23, 2004.FIELD OF INVENTION[0002]The present invention relates to a system and method for sensor less magnetic field control of a motor, such as a stepper motor.BACKGROUND OF THE INVENTION[0003]A motor may operate without any position feedback and rely on a motor's inherent characteristics to control the position of the rotor by energizing particular stators of the motor. This manner of motor operation may typically be found in stepper motors, wherein the rotor of a motor rotates by a specific number of degrees in response to input electrical signals to energize particular stators of such motors.[0004]Stepper motors typically convert digital pulse inputs to analog output rotor movement. Typically, in response to an input pulse of electrical signal, the rotor of a stepper motor rotates by a design-specified number of degrees, or a step. Stepper motors are typically classified as perma...

AI Technical Summary

Benefits of technology

[0024]The motor controller may switch from open loop mode to phase locked loop (or closed loop) mode and back again at a threshold speed. These transitions may be performed with minimal torque disturbance an with no position loss. The motor controller may continually track and accumulate any position related errors and recover the errors when load and speed conditions permit.

Problems solved by technology

Operating stepper motors without any position feedback may cause problems in situations where the rotor “lags” behind the intended rotor position by being a number of steps, or in steps being “lost” and never recovered if the rotor lags behind the intended position too much.

Further, without any positional feedback, resonance problems may occur leading to a “stall” condition, such as when the magnetic field created by the stators of the motor is such that it holds the rotor in place rather than rotating it, cannot be detected and corrected by a motor controller.

Additionally, even if resonance does not lead to a stall conditions, undesirable oscillations would result from the resonance.

Positional feedback sensors may be incorporated into a motor to monitor the position of the rotor optically, but such systems may be complicated to install and maintain, and furthermore may require substantially more control circuitry or software modules to implement.

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